I. Field of the Invention
The present invention is directed generally to equalizing the axle loading of multi-axle vehicles of a working class associated with transporting rather heavy loads which may not be uniformly carried by or distributed among the several axles. More particularly, the present invention involves tag axle assemblies capable of being moved between a first position in which the wheel, or wheels, of the assembly are elevated and a second lowered or load bearing position in which the wheel, or wheels, engage the ground. The improved tag axle assembly of the present invention is specifically designed to be accommodated by the tailgate structure of a rear-loading trash compacting refuse truck to provide auxiliary support to prevent overloading of the rear axle of the truck and to better distribute the relative weight carried by all axles of the truck assembly.
II. Description of the Related Art
Retractable load support devices known as tag axle, tandem axle, or auxiliary axle assemblies are well known in the realm of work vehicles and particularly in hauling vehicles adapted to carry loads of widely varying weight and bulk. The use of downwardly deployable auxiliary or tag axle assemblies makes it possible for such vehicles to add axles and carry more weight--yet comply with regulations governing the legal weight such vehicles can carry over state and federal highways. It has generally been the practice to design tag axle assemblies so that the wheels can be placed in a ground engaging, truck supporting position when desired and elevated and stowed in a manner which does not otherwise interfere with the operation of the vehicle at such times as the tag axle support is unnecessary.
Devices to assist vehicles in meeting load limit restrictions include, for example, those illustrated and described in U.S. Pat. Nos. 4,705,133 and 4,762,421 by Ronald E. Christenson, the inventor in the present application, and Garwin D. McNeilus. Both of these prior patents are assigned to the same assignee as the present invention. These patents are of interest inasmuch as they illustrate tag axle assemblies which extend from the rear of a vehicle and are pivoted between a first or ground engaging position and a second elevated or stowed position. Extended reach tag axle assemblies such as those illustrated by the cited references, for example, generally incorporate a suspension operated by an hydraulic cylinder in conjunction with an hydraulic accumulator to provide the means to raise and lower the tag axle system. In addition, such systems have generally been concerned solely with adding an additional axle for the sake of reducing the per-axle loading below a legal limit so that the hauling or work device of interest does not exceed a legal loading limit when operated on a public highway. Such systems direct little or no concern to redistributing the total weight of the load to not only relieve some of the weight load from an adjacent axle, but also to add overall stability to the loading with respect to the entire vehicle.
Certain hauling vehicles commonly include a truck chassis fitted with a body that is specifically designed for a given task. In the case of refuse trucks, this includes devices for receiving, compacting and discharging refuse materials. One very successful design of such custom-made truck bodies includes a refuse container reservoir accessible for loading and discharging from the rear of the vehicle. This system includes a rear refuse receiving hopper designed to be swept by an hydraulic compacting mechanism which repeatedly compacts the refuse after each loading. In this manner, the refuse eventually fills the available useable reservoir volume extending from the front end back toward the rear of the body until no more material can be compacted. Such a vehicle is generally further illustrated and described in U.S. Pat. No. 3,739,927 and any necessary details from that description may be deemed to be incorporated herein by reference.
It will further be appreciated with regard to refuse hauling trucks of the class described that the loading trough area or tailgate hopper in the rear of the truck extends for a considerable distance behind the rear or drive axle assembly of the vehicle. When this area is full, the compacting mechanism is actuated and it traps this material and sweeps it into the main body storage container of the refuse hauler. The tailgate itself is fabricated of heavy-duty steel assemblies and the compactor mechanism includes large hydraulic cylinders and pushers which have considerable weight. The weight of the tailgate assembly and mechanism make the truck chassis quite heavy even when it is empty. As refuse is loaded and compacted in the refuse hauler, the majority of the payload weight remains acting on the rear or drive axle assembly such that a full load usually cannot be hauled without causing the rear axle loading to exceed the legal limit.
In addition, conventional hydraulic ejector mechanisms for rear-loading refuse hauling vehicles are actuated by longitudinally disposed telescoping cylinders mounted beneath the refuse holding body. These containers further require an ejector configured to fully eject the contents of the refuse holding container including the tailgate area; and, at the same time, the design must accommodate the hydraulic cylinder therebeneath. To meet these requirements, ejectors are designed such that the bottom portion of the ejector mechanism describes a front to rear incline which extends a considerable distance into the lower front portion of the useful reservoir or volume of the truck. This also causes the center of gravity of the load to be shifted rearward toward the drive axle.
The combined effect of the rather extended overhang with regard to the tailgate portion of the truck body, the heavy mechanical components, and the front void space associated with the ejector mechanism, result in more than the desired amount of the weight being carried by the rear axle assembly. Not only does this result in possible overloading of the rear axle assembly, but it also may result in an underloading of the front axle and instability with regard to the front portion of the vehicle as the load tends to tip the entire vehicle rearward.
Certain known previous solutions to this problem have included the use of an additional downwardly deployable axle forward of the rear driving axle, or axles. This successfully reduces the overload weight on the driving axle, or axles. However, because this additional axle has been located forward of the center of gravity of the payload, only part of the force actually functions to reduce the weight on the rear axle. The remaining force operates to reduce the weight on the front steering axle. This characteristically does not allow the front steering axle to be loaded up to the allowable axle weight limit to aid in producing a balanced load. The total weight of the vehicle still cannot reach its allowable limit because of the relatively lighter load on the front axle. The load thus remains with an undesirable rearwardly directed bias.
In addition to extending a fairly large distance behind the rear driving axle assembly of the refuse hauler, the tailgate portion is generally located relatively low to the ground for easy dumping of refuse cans or the like into the hauler receiving area at the very rear of the tailgate assembly. Because of this peculiarity, conventional tag axles, which require a rather large amount of vertical clearance to operate, will not fit under the trough or bucket portion of the tailgate because of its proximity to the ground. Also, the trough or bucket portion of the tailgate of the rear-loading refuse hauler extends from side to side of the hauler extending its close proximity to the ground nearly the full width of the truck thereby precluding the application of a conventional continuous axle tag axle assembly.
Accordingly, to alleviate these and other problems described with regard to rear-loaded, refuse hauling vehicles and other vehicles having similar load distribution characteristics, it is a primary object of the invention to provide a simple, practical mechanism to both assist in supporting the load behind the rear axle assembly of the vehicle and to, at the same time, stabilize the entire loaded vehicle with respect to distribution of the load among the several axles.